The VP5 and VP8 cleavage subunits of the VP4 outer capsid protein of human rotavirus strain KU (VP7 serotype 1), DSI (VP7 serotype 2) or asymptomatic human rotavirus strain 1076 (VP7 serotype 2) were expressed in E. coli. Immunization of guinea pigs with the VP5 or VP8 protein of each strain induced antibodies that neutralized the rotavirus from which the VP4 subunits were derived. The results obtained by cross-immunoprecipitation and reciprocal neutralization assay using antisera to the VP5 and VP8 expressed proteins suggest that the VP8 subunit of VP4 contains the major antigenic site(s) responsible for serotype-specific neutralization of rotavirus via VP4, whereas the VP5 subunit of VP4 is responsible for the cross-reactivity observed among strains that belong to different VP4 serotypes.